Tailings Disposal Options for the Kensington Mine
at Berners Bay Near Juneau, Alaska

Authors

Objective

The Kensington Gold Mine, located
45 miles north of Juneau (Figure 1), Alaska, has been
inoperative since 1937. Coeur Alaska, the sole owner and operator, has
spent $25 million (Richins, pers. comm.) on environmental and biological
research in regards to a planned re-opening in order to find the most
environmentally and economically feasible plan of operation. The most
recent environmental impact statement (EIS) which is pending completion,
and will be available in January 2004, will concern the current plan of
operations. In this paper we will examine the history, economics, and
politics of the mine and discuss the marine science relevant to a submarine
tailings disposal option in the Lynn Canal compared subaqueous disposal
in Lower Slate Lake (LSL).

Introduction

Berners Bay is also located
approximately 45 miles north of downtown Juneau (Figure
2). Four rivers, the Antler, Gilkey, Lace, and Berners rivers, reach
Lynn Canal at the bay and create a delta expanding seaward. The glacial
terrain of Lion's Head Mountain and the valley below support a vast biological
ecosystem of rich flora and fauna, and the accompanying waters of Berners
Bay and the Lynn Canal (as well as numerous streams and lakes) provide
ideal habitat for southeast Alaskan marine and aquatic species. Once covered
by glacial ice, the area is continually isostatically rising and changing
geologically. Still pristine, the Berners Bay area supports recreational
activities such as hiking, fishing, and boating, and is important in the
view of many southeast Alaskan residents.

The area also harbors a valuable deposit of gold ore.
Historically mined by the deserted Jualin and Kensington mine sites (Figure
2), the mining corporation Coeur Alaska, Inc. (Coeur) now owns all
of the mineral rights to the area and plans to re-open the Kensington
Mine on current Forest Service land. The mine is planned to operate for
approximately 12 years, potentially processing 2,400 tons of ore per day
(Hall, pers. comm.). Under the currently proposed plan, mine tailings
from the operation will be deposited in a natural glacial lake near the
mining site. Mine tailings are the waste left after the ore minerals are
extracted, consisting of finely ground waste and ore minerals. Roads and
stream crossings will be built to and from the site of tailings deposition,
and the necessary structures built in and around wetland areas. The necessary
federal, state, and local permits for all of these concerns have been
obtained twice by Coeur Alaska; currently, the disposal of the operation's
mine tailings is the company's biggest issue. Therefore, the disposal
of potentially toxic tailings will be the main concern of this paper.

Kensington Gold Project Details

The Kensington mine was in operation from 1887 until 1937. Coeur is the mining corporation that has owned a portion of the mine since 1987, and has been the sole owner/operator since 1995. Coeur was permitted to reopen the Kensington in 1992 and 1998, but at both those times the methods proposed to remove the gold were not economically feasible. Currently a new mining technique is being analyzed by environmental engineering consultants to obtain the necessary permits. Various plans have been proposed for the disposal of mine tailings including dry tailings disposal, submarine tailings disposal, and subaqueous tailings disposal. The most recent plan, for which an EIS is pending release, proposes the latter method.

Permitted Plan

The Kensington Gold Mine is currently under permit to operate as an underground mine, with a mining process that includes underground primary crushing, surface grinding, and conventional flotation. The mine would be capable of producing up to 2,400 tons of ore and 400 tons of waste rock daily (Hall, pers. comm.). The ore would be concentrated through a chemical and physical flotation process, and the flotation concentrate would be shipped off-site for further processing. Up to 25 percent (US Forest Service, 2002) of the mine tailings would be combined with cement to form a paste, then used to backfill the underground mine openings during operations. The remaining tailings would be trucked to the dry tailings facility (DTF). This facility would be built on 150 acres of wetlands. The DTF would consist of thoroughly dried stacks of tailings, covered in clay to minimize seepage. Seepage and runoff from the DTF would be collected in a sediment pond and discharged into Camp Creek. Approximately 170 employees, brought in by helicopter, would stay at the mine for 10 to 14 days. The total surface disturbance (or footprint) during operations would be 268 acres, including facilities for loading and unloading supplies at Comet Beach on the Lynn Canal (US Forest Service, 2003b).

Proposed Plan

Because of the current economics of gold mining and environmental concerns, Coeur has proposed modifications to the original plan of operations. Access to the project would be shifted from Comet Beach on Lynn Canal to Slate Creek Cove in Berners Bay and surface operation from the Sherman Creek drainage to the Johnson Creek drainage near Berners Bay. The new plan would also convert Lower Slate Lake (LSL) to a tailings storage facility, rather than using the dry tailings facility. A tunnel would be built connecting the Kensington workings to the Jualin Mine land holdings, through which the Kensington would be accessed. The new plan would reduce the overall disturbance footprint from 268 to less than 200 acres. Flotation concentrate would be shipped off-site for processing and mine drainage would be treated at Kensington facilities, as with the current plan of operations (US Forest Service, 2002).

In order to convert LSL to a tailings storage facility, a concrete-faced dam would be constructed before the outlet of the lake to ensure that, as the tailings cover and raise the lake bottom, they are covered by a constant minimum depth of 20 feet. LSL would grow to cover approximately 58 acres, 38 more than the current 20 acres that the lake covers (Richins, pers. comm.). The tailings storage facility would be sized to accommodate approximately 4.5 million tons of tailings (US Forest Service, 2003b), as well as to include adequate routing for the maximum flood (US Forest Service, 2002). The tailings would reach the lake as thickened slurry from the mill via a 3.5-mile gravity-fed pipeline. The pipeline would be less than 12 inches in diameter and run along a 20-foot-wide service road connecting the mill facilities with LSL (US Forest Service, 2002). Flow sensors would be installed to detect any blockages or breaks in the system.

The LSL would act as both a tailings storage facility
(TSF) and a settling pond. The discharge from LSL to East Slate Creek
would be made to mimic the existing hydrology of the stream system (US
Forest Service, 2003a) and would be required to meet Alaska's water quality
standards (US Forest Service, 2002). Water would be pumped from the pond
near the back end of the TSF to the spillway inlet for discharge (US Forest
Service, 2003b). Water from the TSF would also be recycled for use in
the process facilities at an average rate of 150 gallons per minute. At
the end of mine operations, LSL would be reclaimed. Reclamation objectives
are to return to the land to a fresh water lake similar to that of pre-development.
The lake is to be made capable of sustaining a habitat for Dolly Varden
(Salvelinus malma). If necessary, the fish would be reintroduced from
Upper Slate Lake (US Forest Service, 2003a).

The employee camp would be replaced by a method of ferrying
employees daily between marine facilities in Slate Creek Cove and Cascade
Point. The employees would take a bus between Cascade Point and Juneau.
A small landing point at Slate Creek Cove and a 5-mile access road to
the Jualin mine site are already present and would be simply upgraded
to handle traffic. The Slate Creek Cove marine facilities would include
an earthfill ramp and floating platform system designed for barges, which
would deliver an average of seven times per week (Richins, pers. comm.).
The Cascade Point facilities would be constructed on private lands (US
Forest Service, 2002). The footprint of the mine wiould cover privately
and publicly owned lands, as well as lands owned by the Forest Service.

Environmental damage due to stream crossings, watershed disturbance, road
and ferry access, noise pollution, and visible mine structures are already
sanctioned; the appropriate permits have already been approved by the
Environmental Protection Agency (EPA), Department of Natural Resources
(DNR), and Department of Environmental Conservation (DEC). The issue considered
in this report is the method of tailings disposal.

Major Applicable Rules and Regulations

The State of Alaska Department of Environmental Conservation (DEC) and the federal Environmental Protection Agency (EPA) introduce standards and regulations that will affect the how and when of the Kensington re-opening. DEC water quality standards state that lake waters may not exceed 5 nephelometric turbidity units (ntu) above natural conditions, and all other freshwater bodies supporting aquaculture may not exceed 25 ntu (DEC Water Quality Standards, 2003). The EPA prohibits submarine tailings disposal (George, pers. comm.). Because of this, under most circumstances submarine tailings disposal is never an option for mining operations to consider. However, the feasibility of submarine tailings disposal is almost entirely dependent on specific cases (Tomich Kent, pers. comm.), and in the case of the AJ Mine Project in Juneau, AK, the EPA granted an exemption to the Echo Bay Mining Co. and agreed to extensive studies and research that could lead to approved submarine tailings disposal (US EPA, 1996). In this instance, for EPA consideration it had to be shown that submarine tailings disposal is the most environmentally sound option through extensive analysis including physical, chemical, and geological oceanography and sedimentation information of the area in question (Echo Bay Mines, 1995).

A corporation such as Coeur must also obtain a National Pollutant Discharge Elimination System (NPDES) permit from the EPA prior to operation. Coeur Alaska has already obtained an NPDES permit, but modifications must be made according to the new plan of operations (George, pers. comm.). The company must also modify their official plan of operations; release a supplemental Forest Service EIS; amend the Large Mine Permit, DEC Solid Waste Permit, and permits involving water discharge pipes from LSL; and obtain DEC certifications for the zone of tailings deposition (Coeur Alaska Group, 1998).

Economic History and Future

Coeur Alaska has already spent over $150 million on the Kensington Project (Richins, pers. comm.). The re-opening of the Kensington Mine will be a great boost to southeast Alaska's economy, as it will employ about 225 permanent workers (Alaska Department of Natural Resources, 2003), along with many additional support sector employment opportunities: approximately 180 additional indirect jobs will be created (USFS/McDowell Group, 1990; Richins, pers. comm.).

Four hundred two state jobs will be lost under Governor
Murkowski's 2003 budget plan (Inklebarger, 2003) and mine-related
employment can help to offset the losses as a promised 95% of the work
force will be Alaskan citizens (Bigsby, 2003) averaging a wage of $50,000
a year. The payroll of the proposed project will be an annual $16 million
(Richins, pers. comm.) The jobs created would increase basic industry
employment in Juneau from between 1.9% and 5.7% (US Forest Service/McDowell
Group, 1990). In 1992, the Kensington Gold Mine project record of decision
was approved with the estimated project cost at $210 million, and an operating
cost of $282/oz of gold (ADNR, 2003).

The newly proposed project will save the company around $60 million; the
cost of operation will be about $155 million (Richins, pers. comm.). It
will last at least 12 years: 2 years for construction and startup, 8 years
for gold recovery, and two years for active reclamation (Richins, pers.
comm.). The corporation will spend at least $7.5 million for direct local
purchases during construction and $13.5 million during operation.

The cost of gold in 1988 was $500/oz, whereas in 1998 it was $220/oz (Richins,
pers. comm.). This drop was so drastic that it compromised the feasibility
of the mine; Coeur was not able to operate efficiently enough to profit
under the on-land disposal plan of operations that had been permitted.
But with a rise in price to $300/oz in 2000, the mine was again proposed–with a few changes. Production would be lowered from 4,000 tons
per day to 2,400 tons per day (Hohensee, pers. comm.) to render the mine
less dependent on gold prices (current prices are around $400/oz), and
instead of storing dry tailings in a facility on land (as the previously
permitted plan had required), subaqueous tailings disposal in LSL was
proposed. Both submarine and subaqueous tailings disposal cost $0.10 per
ton of waste, thus both disposal systems are equally economically preferable
to on-land disposal systems of any sort.

Other Alaskan corporations establish a background for the Coeur d'Alene
mining operations in southeast Alaska. The Cape Fox Land Adjustment Act
of 2002, Senate Bill (SB) 2222 proposed by Alaska senator Frank Murkowski,
proposes a land-swap that would "consolidate Cape Fox, Sealaska
and Tongass National Forest surface and substrate estates and simplify
Forest Service boundaries." (Richins, 2002) Currently, the surface
of the land in question is owned by the Forest Service, while the mining
rights to the subsurface area is privately owned by Coeur.

Under SB 2222, Sealaska, the regional native corporation for southeast,
would trade the 8,200 acres on Prince of Wales Island received under the
original Alaska Native Claims Settlement Act for approximately 9,300 in
the Berners Bay area. Cape Fox, the regional native corporation for Saxman
would give up 2,900 acres of marginally logged land near Ketchikan for
2,700 acres of area near Berners Bay (Alaska Journal of Commerce, 2003).
If the proposed SB 2222 is passed, Coeur will pay land lease payments
to the native corporations, as opposed to the federal government.

The Ore Body and Tailings

The gold deposit in question
occurs within a structurally sheared portion of rock. The body has low
sulfide content and is thus net neutralizing (not acid generating); the
material does not pose a significant risk of Acid Rock Draining (ARD).
Gold occurs in quartz veins in four states: in the mineral calaverite,
as native gold, as inclusions in pyrite, and along microfractures (Robinson,
pers. comm.). Studies have detected trace amounts of tellurite (TeO2),
coloradite, (Ag3AuTe2) and altaite (PbTe) (Dave Cox, pers. comm.).

Ecological Assessment: Lower Slate Lake; Subaqueous Tailings Disposal

Potential Contaminants

According to the Forest Service's Ecological Risk Assessment of Aqueous Tailings Disposal at the Kensington Mine, the only chemicals of potential ecological concern (COPEC) to consider for the Berners Bay tailings disposal plan are chromium, aluminum, pH and total suspended solids (TSS) or turbidity (Tetra Tech Inc., 2003). In aqueous conditions, the toxicity of aluminum depends on the pH of the water. Aluminum and chromium, as bioaccumulative metals, can travel through the food chain and cause disease and death to fish as well as other predators when accumulated in the tissues of fish and other prey. Aluminum is found naturally in sediment, while chromium is introduced when chromium steel equipment is worn from use (Robinson, pers. comm.). Natural lake sediments have similar to greater amounts of aluminum, so post-operational recovery from aluminum-containing sediment is of little concern. Leach tests indicate that there is essentially no mobility of metals to water (US Forest Service, 2003a).

Acid rock drainage (ARD) is not an environmental hazard
in the Kensington Mine situation because the proposed Kensington ore body
has insignificant ARD potential–the rock in the area is very low
in sulfides (Hohensee, pers. com.), the only sulfides being in traces
of pyrite (Connor, pers. comm.). The deposition of tailings in LSL will
raise the pH of the lake to an estimated 7.8, well within the range deemed
acceptable by the Forest Service of 6.0-9.8 (Tetra Tech, 2003). The possibility
of heavy metals leaching from discharged tailings in any body of water,
LSL or the Lynn Canal, is negligible as the tailings placed deep underwater
lack the oxygen contact that aids in liberating metals from ore in terrestrial
evironments.

Total suspended solids is an unavoidable issue concerning sub-aqueous
tailings disposal. Under the current plan, tailings slurry deposited in
Slate Lake will raise the turbidity of the lake past the DEC water quality
standards during the time which the mine is in operation. However, at
the point of outlet, the water in Slate Creek, and thus the water flowing
from Slate Lake into Berners Bay, does meet DEC standards due to settling
and dilution.

The 1998 Kensington Mine proposal called for onsite gold extraction, a
process that could introduce cyanide into the surrounding environment.
However, the revised proposal of 2002 includes off-site shipment of concentrated
material containing gold ore for processing at facilities outside of Southeast
Alaska. This eliminates the issue of unnatural amounts of cyanide in the
Berners Bay area due to mining activity.

The eulachon (hooligan) run that occurs within Berners
Bay each spring in late April and early May is a major issue concerning
the disposal of mine tailings. The eulachon are small fish with over 20%
body fat, and the Berners Bay run of 10 to 20 million fish (Hall, pers
comm.) provides predators with needed energy to begin the mating season.
An estimated 300 to 600 sea lions utilize a haulout within ten miles of
the bay, and 1,000 more within forty miles north (Hall, pers. comm.),
and before breeding the animals gather in Berners Bay to feed. Approximately
1,000 sea lions, 40,000 gulls, 600 eagles (Hudson, 2003) and numerous
other species gather for each eulachon run, and any actions detrimental
to the run would have dire consequences on such a vast amount of predators.
The east fork of Slate Creek runs from LSL into Berners Bay, and while
water out of LSL would meet DEC water quality standards, any material
leaving the lake through the creek would empty into the shallow area of
the delta used by small fish, including the eulachon.

Approximately 20 acres of wetland area will be affected under this proposal.
There will be a net gain of aquatic habitat; LSL will increase from 20
to 58 acres, forming a larger, shallower lake. This change will be beneficial
to aquatic systems in the area, as at present much of the lake is too
deep for light to penetrate and is an unproductive habitat (Richins, pers.
comm.). No permanent habitat loss to fisheries are anticipated to be suffered
(Kline, pers. comm.), however areas of wetland will be used for construction,
and acres will be submerged as the lake expands.

Ecological Assessment: Lynn Canal (Submarine Tailings Disposal)

Physical Factors

The possible submarine tailings
disposal system will deposit tailings in Lynn Canal. The canal occupies
a 93-mile flooded glacial fjord with maximum width of 12 miles. The substrate
is soft at depths greater than 36 ft. and flat, with a bottom depth of
650-980 ft. Tides, freshwater sources, and wind primarily control water
circulation in the canal, varying depending on relative location along
the canal. Freshwater input is due to rivers, streams, and precipitation,
which at its highest input during the summer and fall creates great estuarine
circulation. Tidal amplitudes near the proposed site range up to 24.6
ft., and there is a constant general movement of fresh surface water away
from shore and deeper waters toward shore (Coeur Alaska Inc., 1998). The
substrate has similar elemental components to the tailings; composition
of tailings vs. marine sediment is shown in Figure 6.

While it is improbable that tailings will reenter the water column because of their density and the lack of sufficient current in the deeper parts of the Lynn Canal (Scott W. Johnson, pers. comm.), it is not impossible, as in the case of the Island Copper Mine in Vancouver, British Columbia. After being deposited in the ocean through an submarine tailings disposal system, tailings reentered the water column, becoming visible from shore and even washing up on the beach due to seasonal upwelling events (Moore, 2002). Shallow productive coastlines and areas with strong currents are therefore unacceptable deposition locations, as the risk of tailings re-circulating into the water column is increased (Ellis, 1982). Along the Lion's head mountain shoreline, the Lynn Canal reaches a depth of 600 ft. within approximately 4,000 feet of shore. The Echo Bay Mines company proposed depositing tailings in a fjord at a depth of 600 to 700 ft. (Johnson, pers. comm.), a depth reached easily from the Kensington Mine site by a gravity-fed pipeline.

Lynn Canal substrate harbors a plentiful benthic community,
the level of creatures that would be most effected by an SUBMARINE TAILINGS
DISPOSAL system at Kensington. The most prevalent danger to the benthic
community under an SUBMARINE TAILINGS DISPOSAL system is the smothering
of organisms living within the sea-bottom sediment. Benthic fauna burrow
into and feed off of marine sediment, and form the primary food source
for many other bottom-dwelling organisms, such as the commercially important
king crab. Benthos in areas receiving high rates of tailings deposition
can be eliminated or displaced (Kline, 1998) as they cannot adapt to constant
and heavy sediment deposit. However, Kline (1996, 1999) showed that the
recolonization of sediment by benthic fauna and marine invertebrates (respectively)
would not be influenced by the presence of deposited gold mine tailings;
figure 5 illustrates their comparable benthic habitabilities.
The benthos that inhabit the bottom sediment form the primary food source
for other bottom-dwellers, and therefore present a potential problem to
all organisms in the food chain if they become contaminated. The most
probable pathway through which commercially harvested fish, crabs and
other important organisms such as the eulachon and their predators can
become contaminated as a result of submarine tailings disposal is through
the food chain (Adam Moles, pers. comm.). Therefore, if any contamination
threat to benthos is probable, submarine tailings disposal should not
be regarded as the most environmentally sound option.

Other bottom-dwelling organisms with potential to be directly affected
by submarine tailings disposal are Pacific halibut (Hippoglossus stenolepis)
and yellowfin sole (Pleuronectes asper) (S.W. Johnson et. al., 1998).
These flatfish are both commercially important and sensitive to seas floor
changes, as they burrow into and ingest soft sediment (Moles, pers. comm.).
A 1998 study by S.W. Johnson, S.D. Rice, and Dr. Adam Moles showed that
the preference of yellowfin sole of natural marine substrate over fresh
and weathered gold mine tailings was behavioral; tailings material became
so compact in the ocean environment that benthos were unable to burrow
into them, thus forcing them to choose a softer substrate. Some tailings
form a concrete-like layer in the ocean, but some do not; the probable
density of the substance post-deposition can be changed pre-deposition
by laboratory methods (Scott W. Johnson, pers. comm.). The 1998 study
also showed that the fish preferred equally the natural sediment and tailings
sediment that had been covered by as little as 2 cm of natural deposit;
this suggests that the natural burial of tailings in an area of high sedimentation
would lessen any temporary effect. An area such as this could be found
at the mouth of one or several large rivers, such as the rivers in Berners
Bay contributing to the expanding delta.

Other organisms potentially affected by tailings sediment are king and
Tanner crabs, which, similar to flat fishes, ingest sediment while feeding.
Tanner crabs (Chionoecetes bairdi) inhabit deep water up to 500 feet and
are harvested by personal use and commercial fisheries. In a 1997 study
by R.P. Stone and S.W. Johnson, Tanner crabs held for 500+ days on weathered
tailings showed no differences in survival or growth than those held on
reference material, and the metal burden of each tissue sample was similar.
However, this test refers to old mine tailings; fresh tailings may leach
metals, especially if deposited in an area with available oxygen. The
area of the Lynn Canal in close proximity to the proposed mine site accommodates
commercially harvested king and Dungeness crab (Focht, pers. comm.) that
could be affected.

Important commercial fish in and around Berners Bay such as pink and chum
salmon inhabit the higher zones of the ocean, and while they would not
be affected directly by the tailings if they were to remain on the ocean
floor, circulation of tailings could affect commercial fishing harvests
in the area. Salmon and other fish are unlikely to be contaminated directly
by mine tailings, as tailings will presumably be confined to a specific
area of the Lynn Canal, and juveniles going to sea will not be exposed
for long periods of time to any tailings (Focht, pers. comm.). A potential
problem would arise if tailings were to settle near a salmon spawning
or hatching area, or drift far into Berners Bay and contaminate the eulachon
population. The average annual net value of the Lynn Canal alone between
1991 and 1997 was $3.62 million (Coeur Alaska Inc., 1998)–an indispensable
economic resource. Possibly more dangerous to the commercial fishing industry
than the physical threat of contamination are the marketing implications
(Focht, pers. comm.). Alaskan-caught fish are marketed as 100% natural,
and in the consumer's eye the quality of the product could decrease
significantly with the introduction of mine tailings to the population.

Under a SUBMARINE TAILINGS DISPOSAL plan, less wetland
habitat will be affected than under the LSL tailings storage plan (Richins,
pers. comm.). Kensington tailings have been proven inert and very close
in elemental and mineral composition to natural Lynn Canal sediment (Figure
4 ) (Kline, Richins, pers. comm.); in conclusion, toxins are of insignificant
concern.

Conclusions and Recommendations

We conclude that the currently proposed plan of operations is not the most environmentally sound procedure; with accordance to further research, we recommend that the main mine waste product, the mine tailings themselves, be deposited in the ocean through a submarine tailings disposal system.

According to a study conducted by the U.S. Bureau of
Mines, the right combination of conditions can render the environmental
impacts of submarine tailings disposal minimal. These conditions include
that: the percentage of sulfide minerals in the ore is low; no easily
dissolvable toxic substances occur within the ore body; non-toxic reagents
are used in the mill; milling does not generate secondary toxic products
introduced into an environment; slurry is deposited with minimal amounts
of water to reduce submarine transportation; tailings are deaerated (mixed
with air and seawater to suspend tailings fines, to be released, and to
minimize density differences between slurry and seawater) before entering
the ocean; the density of liquid in tailings is equal to water density
at the depth of disposal; tailings outfall is effectively placed; and
the environment in which tailings are deposited is stable (Baer et al.,
1995).

Past research shows that the Kensington Mine area has exceptional opportunity
to undertake a submarine tailings disposal system with minimal impact
to the environment. We believe submarine tailings disposal is a favorable
option to subaqueous tailings disposal in LSL. Concerning the proposed
Kensington area, and according to the above standards, we can justify
Lynn Canal disposal because: (1) The Kensington ore body has an extremely
low level of sulfides and sulfide compounds that contribute to toxicity
and ARD potential; (2) the only potentially toxic COPECs are chromium
and aluminum, both of which occur in very small amounts, and, if properly
placed, will pose no risk to organisms above benthic level, a proven small
or negligible risk to crabs and flatfish, and have no observed effect
on benthic recolonization of the sediment; (3) no toxic reagents will
be employed at the Kensington site, as ore will be shipped elsewhere for
processing; (4) the topography of the Lynn Canal lends itself to deep
submersion of tailings, therefore minimizing the possibility of tailings
spreading on the ocean floor or reentering the water column; (5) all tailings
slurry conditions discussed above can be feasibly induced on-site.

We recommend that the EPA grant Coeur an exemption, as they considered
in the case of the Alaska-Juneau Mine, so that they might utilize a submarine
tailings disposal system as opposed to the subaqueous tailings disposal
plan currently proposed. We suggest intense research concerning topography
and current circulation in the Lynn Canal in order to find a deep, fairly
contained area in which to deposit tailings through a gravity-fed pipeline
leading from slurry storage on-site at the mine to the chosen deposition
site underwater. Natural sedimentation deposition should also be considered,
as constant and relatively heavy natural deposition hastens the recolonization
of deposited tailings. Necessary structures for an SUBMARINE TAILINGS
DISPOSAL system would include a gravity-fed pipeline from the mill down
Lion's Head Mountain directly to a depth of at least 600 ft. (and
well below photic zone) in a chosen submarine area; and a deaeration,
or mixing, chamber near the shore pre-deposition. Remaining processing
water should first be drained from tailings; then tailings may be transported
by gravity through pipeline over land to the mixing tank. Water for these
mixing tanks may be taken in from pipes on the ocean floor past 36 ft.
from shore where rocky substrate turns to soft sediment. In determining
deposit placement area and method, engineers should take into consideration
submarine topography, current rates, fauna concentration, amount and velocity
of discharge, and waste density.

It must be especially noted that according to intensive scientific study,
Kensington tailings can be considered inert (Kline, pers. comm.). In the
Lynn Canal area, submarine tailings disposal will only temporarily affect
a uniform and widely spread marine habitat (Kline, 1998). Multiple studies
have shown that tailings "may be disposed of in the ocean"
(Kline, 1998)–Coeur Alaska's Kensington Gold Project represents
a realistic opportunity to utilize submarine tailings disposal as the
most environmentally and economically feasible option in a sound plan.